Fix blur with alpha looking wonky

[ErikReider]

We probably would need to interpolate between the original texture and the blurred texture when adjusting the alpha of the blur?

Image of alpha 0.9, blur passes 3, and blur radius set to 5:

[WillPower3309]

Hmm this worked fine on swayfx with my animations branch (where we update the blur alpha with the tex alpha for fade in/ out). Wonder what's going wrong here

[nikoloc]

i think this is the issue i have faced. when using low opacity values (set using wlr_scene_buffer_set_opacity()), they would affect the blur as well, so the original background would be seen more than the blur.

i guess you currently do blur by composing it into the buffer. would it be possible to first apply opacity settings to the original buffer, and then compose the blur after? that way seems more natural and i guess it would look better.

edit:

they would affect the blur as well

the way it is now, xray effect is lost when opacity is applied to the buffer, so i think my assumption is correct.